In recent years, demand of high efficiency in cutting has been increased. Accompanying with increase of this demand, a cutting tool having a longer tool life than those of the conventional ones has been required. Therefore, as characteristics required for the tool materials, it is important to improve characteristics relating to lifetime of a cutting tool. For example, it is more important to improve wear resistance and fracture resistance of the cutting tool. To improve these characteristics, a coated cutting tool which comprises a substrate such as a cemented carbide, cermet, cBN, etc., and one layer or two or more layers of a coating layer such as a TiN layer, a TiAlN layer, etc., formed on the surface thereof has widely been used.
Thus, various techniques to improve characteristics of such a coating layer have been proposed. In Patent document 1, for example, it has been disclosed a coated cutting tool in which a value Ih/Ic which is a ratio of a sum Ih of a diffraction peak intensity at a (103) plane of hexagonal niobium nitride and a diffraction peak intensity at a (110) plane of the hexagonal niobium nitride with a diffraction peak intensity Ic at a (220) plane of cubic niobium nitride is 2.0 or less when a hard coating layer is measured by X-ray diffraction. The coated cutting tool is disclosed to be excellent in cutting performance of a Ti alloy.
In Patent document 2, it has been disclosed a coated cutting tool in which a value Ic/Ih which is a ratio of a sum Ih of a diffraction peak intensity at a (103) plane of hexagonal niobium nitride and a diffraction peak intensity at a (110) plane of the hexagonal niobium nitride with a diffraction peak intensity Ic at a (200) plane of cubic niobium nitride is 0.05 to 1.0 when a hard coating layer is measured by X-ray diffraction. The coated cutting tool is disclosed to be excellent in lubricity and wear resistance.